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Driven to diffraction

A holographic screen can provide “shocking” improvements in picture quality
for rear projection TV sets, says Thomson of France (WO 99/39512). Normally,
lenses beam red, green and blue light onto a translucent TV screen. But since
the beams hit the screen at different angles, their colours only look pure to a
viewer sitting in front of the set. Adding a segmented “fresnel” lens widens the
viewing angle, but coarsens the image. Thomson has found that a photopolymer
sheet etched with a holographic diffraction grating disperses the light widely
enough for viewers to see pure colour from …